1. Field of the Invention
The invention relates to a synergistic flame retardant combination which comprises salts of 1-hydroxydihydrophosphole oxides and/or 1-hydroxyphospholane oxides and certain nitrogen compounds.
2. Description of the Related Art
Polymers are often made flame retardant by adding phosphorus or halogen compounds, or mixtures thereof, to them. Mixtures of phosphorus and nitrogen compounds as well are often used as flame retardants.
Salts of phosphinic acids have proven suitable as effective flame retardant additives for polymers, as have alkali metal salts (DE-A-2 252 258) and salts of other metals (DE-A-2 447 727).
Calcium phosphinates and aluminum phosphinates have been described as particularly effective in polyesters, and impair the mechanical properties of the polymer molding compositions to a lesser extent than do the alkali metal salts (EP-A 699 708).
Synergistic combinations of alkyl and/or aryl phosphinates with certain nitrogen compounds have a more effective action in a whole range of polymers than the phosphinates alone (PCT/EP97/01664).
Alicyclic phosphinates as well, such as the salts of 1-hydroxyphospholane oxides, have recently been described as flame retardants, especially for polyesters and polyamide (European Patent Application No. 97 102 722.2). The flame retardancy, however, especially in the case of thin-walled moldings for the electrical industry, is somewhat poorer than that of comparable alkyl phosphinates. Nevertheless, the alicyclic phosphinates are less soluble in water than the alkyl phosphinates and are therefore more suited for use in polymeric molding compositions for the electrical industry.
It has now surprisingly been found that by adding nitrogen-containing synergists it is possible very considerably to increase the effectiveness of alicyclic phosphinates, especially in thin-walled moldings, thereby achieving a level of flame retardancy which matches that of the synergistic mixtures with alkyl phosphinates.
The invention thus relates to a synergistic flame retardant combination for thermoplastic polymers which comprises as component A a salt of 1-hydroxydihydrophosphole oxides of the formula (Ia) or formula (Ib) and/or 1-hydroxyphospholane oxides of the formula (II) 
in which
R1 to R4 are hydrogen or C1-C12-alkyl, preferably C1-C4-alkyl, especially methyl or ethyl;
M is a metal from the second or third main group or subgroup of the Periodic Table, such as magnesium, calcium, zinc or aluminum, preferably aluminum, and
l is 1, 2 or 3
and as component B a nitrogen compound of the formula (III) to (VIII) or a mixture of the compounds designated by the formulae 
xe2x80x83in which R5, R6 and R7 can be defined as follows: hydrogen, C1-C8-, preferably C1-C4-alkyl, C5-C16-, preferably C5-C8-cycloalkyl or -alkylcycloalkyl possibly substituted by a hydroxyl or a C1-C4-hydroxyalkyl function, C2-C8-, preferably C2-C4-alkenyl, C1-C8-, preferably C1-C4-alkoxy, -acyl, -acyloxy, C6-C12-aryl or -arylalkyl, preferably C6-C10-aryl or -arylalkyl and also xe2x80x94OR8 and xe2x80x94N(R8)R9 (excluding melamine, R8xe2x95x90R9=H) and also N-alicyclic or N-aromatic. N-alicyclic in this case denotes cyclic heteroalkanes or heteroalkenes having 1 to 2 nitrogen atoms and a ring size of from 5 to 8, preferably from 5 to 6. Examples thereof are pyrrolidine, piperidine, imidazolidine, piperazine or 2,5-dihydropyrrole. N-aromatic denotes heteroaromatic 5- or 6-membered ring compounds which include 1 to 2 nitrogen atoms in the ring, such as pyrrole, pyridine, imidazole, pyrazine, and also condensed aromatic compounds having 9 to 14, preferably 9 to 10 carbon atoms, of which from 1 to 3, preferably from 1 to 2 CH groups can be replaced by a nitrogen atom, such as quinoline, phenanthroline, phenazine.
R8 denotes the following groups: hydrogen, C1-C8-, preferably C1-C4-alkyl, C5-C16-, preferably C5-C8-cycloalkyl or -alkylcycloalkyl possibly substituted by a hydroxyl or a C1-C4-hydroxyalkyl function, C2-C8-, preferably C2-C4-alkenyl, C1-C8-, preferably C1-C4-alkoxy, -acyl, -acyloxy or C6-C12-, preferably C6-C10-aryl or -arylalkyl.
R9, R10, R11, R12 and R13 denote the same groups as R8 and also xe2x80x94Oxe2x80x94R8.
m and n are 1, 2, 3 or 4.
X denotes acids which are able to form adducts with triazine compounds (III) (including melamine), examples being cyanuric acid, phosphoric acid, orthoboric acid, metaboric acid.
In the text below the term xe2x80x9csaltxe2x80x9d denotes salts of 1-hydroxydihydrophosphole oxides and of 1-hydroxyphospholane oxides.
Examples of suitable salts are the alkaline earth metal, magnesium, zinc and aluminum salts of 1-hydroxy-3-alkyl-2,3-dihydro-1H-phosphole 1-oxide, 1-hydroxy-3-methyl-2,5-dihydro-1H-phosphole 1-oxide, 1-hydroxy-2,3-dihydro-1H-phosphole 1-oxide, 1-hydroxy-2,5-dihydro-1H-phosphole 1-oxide, 1-hydroxy-1H-phospholane 1-oxide and 1-hydroxy-3-methyl-1H-phospholane 1-oxide, and mixtures of these salts. The aluminum salts are preferred.
The salts can be prepared from the 1-hydroxydihydrophosphole oxides and 1-hydroxyphospholane oxides by known methods in which it is possible to employ, in aqueous solution, the metal carbonates, metal hydroxides or metal oxides. The 1-hydroxydihydrophosphole oxides are obtainable by known methods from the 1-chlorodihydrophosphole oxides, which can be prepared, for example, in accordance with EP-A-0 452 755. The 1-hydroxyphospholane oxides can be prepared from these by hydrogenation.
Polymers for the purposes of the invention are also described in the application PCT/EP97/01664 on pages 6 and 9, the content of which is expressly incorporated herein by reference.
The amount of the salts to be added to the polymers can vary within wide limits. In general use is made of from 1 to 30% by weight, based on the finished polymer compound. The optimum amount depends on the nature of the polymer, on the nature of component B and on the type of salt employed itself, and can easily be determined by experimentation. Preference is given to from 3 to 20, in particular from 5 to 15% by weight.
The salts of the invention can be used in different physical forms depending on the nature of the polymer used and on the desired properties. Thus in order to obtain a better dispersion in the polymer, for example, the salts can be ground into a finely divided form. If desired, it is also possible to employ mixtures of different salts.
The salts of the invention are thermally stable, and neither decompose the polymers in the course of processing nor influence the process of producing the plastics molding composition. The salts are nonvolatile under preparation and processing conditions for polymers.
As component B the synergistic flame retardant combination comprises a nitrogen compound of the formula (III) to (VIII) or a mixture of the compounds designated by the formulae.
Formula (VII) denotes adducts of the triazine compounds (III) (including melamine) with appropriate acids, where m and n can each be 1, 2, 3 or 4. Examples of such compounds are melamine cyanurate, melamine phosphate, dimelamine phosphate, melamine pyrophosphate and melamine diborate.
As component B it is likewise possible to employ oligomeric esters of tris(hydroxyethyl) isocyanurate with aromatic polycarboxylic acids, as are described in EP-A 584 567.
It is likewise possible as component B to employ nitrogen-containing phosphates of the formulae (NH4)yH3xe2x88x92yPO4 and (NH4PO3)z, where y can adopt numerical values from 1 to 3 and z is an arbitrary number which, in addition, is typically the average value of a chain-length distribution.
Preferred nitrogen compounds in the context of the invention are benzoguanamine (formula III, R5=phenyl, R6xe2x95x90R7=NH2), tris(hydroxyethyl) isocyanurate (formula IV, R9xe2x95x90R10xe2x95x90R11=xe2x80x94CH2xe2x80x94CH2xe2x80x94OH), allantoin (formula V, R9xe2x95x90R10xe2x95x90R11xe2x95x90R12xe2x95x90R13=H), glycoluril (formula VI, R9xe2x95x90R10xe2x95x90R11xe2x95x90R12=H) and also melamine cyanurate, melamine phosphate, dimelamine phosphate and melamine pyrophosphate (all of the type of formula VII), urea cyanurate (R9 to R12=H; of the type of formula VIII) and ammonium polyphosphate (NH4PO3)2.
The nitrogen compounds employed as component B are prepared, in some cases industrially, by known processes.
The amount of nitrogen compound (component B) to be added to the polymers can be varied within wide limits. In general use is made of from 1 to 30% by weight, based on the finished polymer compound. The optimum amount depends on the nature of the polymer, on the nature of the salt employed (component A) and on the type of nitrogen compound itself, and can easily be determined by experimentation. Preference is given to from 3 to 20, in particular from 5 to 15% by weight.
Preferred thermoplastic polymers are engineering plastics, such as polystyrene-HI (with increased impact strength), polyphenylene ethers, polyamides, polyesters, polycarbonates and blends or polyblends such as ABS or PC/ABS.
Particular preference is given to polyesters, polyamides and ABS polymers.
The flame retardant components A and B can be incorporated into plastics molding compositions by, for example, premixing all of the constituents, as powders and/or granules, in a mixer and then homogenizing the mixture in the polymer melt in a compounder (for example, a twin-screw extruder). The melt is commonly drawn off as a strand, cooled and granulated. Components A and B can also be introduced separately by way of a metering system directly into the compounder.
It is likewise possible to admix the flame retardant additives A and B to finished polymer granules and to process the mixture directly into moldings on an injection molding machine.
In the case of polyesters, for example, the flame retardant additives A and B can also be added to the polyester mass in the course of polycondensation.
In addition to the flame retardant components A and B the molding compounds may also have added to them fillers and reinforcing agents such as glass fibers, glass beads or minerals such as chalk. In addition, the molding compounds may include other additives, such as antioxidants, light stabilizers, lubricants, colorants, nucleating agents or antistats. Examples of the additives that can be used are given in EP-A-584 567.
The flame retardant plastics compositions are suitable for producing moldings, films, filaments and fibers by means, for example, of injection molding, extrusion or compression.